ACTG 888 is a 250-subject, prospective, non-randomized study of discontinuing prophylaxis in HIV-infected subjects who have had a CD4 count <100 cells/mm3 any time in the past and no confirmed PCP, who have had a confirmed episode of pneumocystis at least 6 months prior to study entry (whether or not the CD4 count was <100 cells/mm3). Subjects will be asked to discontinue their PCP prophylaxis if antiretroviral therapy has resulted in a sustained CD4 increase to >200 cells/mm3 on two measurements at least 12 weeks apart. Subjects will be evaluated for symptoms and CD4 counts every 8 weeks; plasma for HIV-RNA will be collected and stored every 16 weeks until the last subject has been on study for 18 months. Subjects whose CD4 cell count has fallen to <150 cells/mm3 will be immediately have the CD4 cell count reevaluated. Subjects whose CD4 cell count has fallen to between 150 and 200 cells/mm3 will have the CD4 cell count reevaluated within 4 weeks. If the second CD4 count is <200 cells/mm3 for either case, conventional PCP prophlaxis will be resumed and the subject will be followed on study. Subjects with symptoms of oral thrush or unexplained fever for >2 weeks, will resume conventional PCP prophylaxis, and will continue to be followed on study.